No. K}.] ECHINODERMS OF CONNECTICUT. 117 



length of the body, and the cut walls folded and pinned back, 

 the arrangement of the internal organs is plainly visible. 



In the spacious body cavity lie the much coiled intestine, the 

 profusely branched respiratory trees, the Polian vesicles, the 

 madreporic canal, and other organs, as shown on Plate XXX. 



At the anterior end of the body the slender esophagus leads 

 from the region of the calcareous ring at the base of the tentacles 

 back to the sac-like stomach. The walls of the stomach are 

 highly muscular and much thicker than the other parts of the 

 alimentary canal. At its posterior end the stomach becomes much 

 narrowed, and leads into the long and much coiled intestine. 

 The total length of the intestine is several times that of the 

 body. It is arranged in three broad loops, each of which is in 

 itself much convoluted (Plate XXX). The first section leads 

 with many folds posteriorly (near the mid-dorsal line) to the 

 dorsal side of the cloaca. Here there is a sharp bend with several 

 convolutions, and the second section leads forward (on the left 

 dorsal side) to the anterior half of the body. After several 

 further twists back and forth through the coelomic space, the 

 third section leads posteriorly (on the right ventral side) to 



EXPLANATION OF PLATE XXX. Anatomy of Holothurian, Thyone briareus. 



(Twice natural size.) 



The body has been opened on the ventral side by a longitudinal in- 

 cision extending the whole length of the animal in the right ventral inter- 

 radius. The body walls and viscera are spread symmetrically on both sides. 

 In the crown of tentacles (0 are seen the two smaller ventral tentacles (f 1 ). 

 From the calcareous ring beneath the tentacles, the slender esophagus 

 (e) leads into the saclike stomach (st), and thence into the intestine. 

 The intestinal convolutions are not represented in exactly their natural 

 positions, but it is possible to distinguish the three main sections (i. I, 

 i. 2, and i. 5) of this canal. The intestine is attached to the body walls 

 by strong mesenteries, of which only one (mes}, connected with the 

 posterior section of the intestine; is represented. The cloaca (cl) is con- 

 nected with the body walls by strong muscles (cl. m) ; its connection 

 with the exterior through the cloacal aperture (cl. ap) is shown. From 

 the anterior end of the cloaca the pair of profusely branched respiratory 

 trees (r. t) extend nearly to the anterior end of the body cavity. The 

 slender filaments of the sexual gland (g) lead to a narrow genital duct 

 (g. d), which opens on the -dorsal side of the body between the bases 

 of the dorsal tentacles. The five pairs of powerful longitudinal muscles 

 (/. m.), which mark the five radii of the body, connect anteriorly with 

 the equally strong retractor muscles (r. m) of the peristome. At 

 the base of the calcareous ring (c. r), beneath the tentacles, the ring 

 canal (r. c) of the water-vascular system is seen. This canal is con- 

 nected with the large saclike Polian vesicles (P. v), and the slender 

 madreporic canal (s. c), the latter ending in a small madreporic plate. 



